That Lh pulsatility is disrupted and that mental and physical performances are degraded abruptly at a particular threshold of energy availability; 2) that this threshold corresponds to a level of energy availablity at which the hormonal regulation of metabolism alters the mobilization and utilization of stored metabolic fuels and reduces resting metabolic rate to compensate for energy deficiency; and 3) that this level of energy availability is higher in women than in men, making women more susceptible than men to the harmful effects of low energy availability.